Q

# Help me understand! A speeding motorcyclist sees traffic jam ahead of him. He slows down to 36 km/hour. He finds that traffic has eased and a car moving a head of him at 18 km/hour is honking at a frequency of 1392 Hz. If the speedof sound is 343 m/s

A speeding motorcyclist sees traffic jam ahead of him. He slows down to 36 km/hour. He finds that traffic has eased and a car moving a head of him at 18 km/hour is honking at a frequency of 1392 Hz. If the speed of sound is 343 m/s, the frequency of the honk as heard by him will be:

• Option 1)

1332 Hz

• Option 2)

1372 Hz

• Option 3)

1412 Hz

• Option 4)

1464 Hz

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As we discussed

frequency of sound when source is moving away and observer is moving towards the source -

$\nu {}'= \nu _{0}.\frac{C+V_{0}}{C+V_{s}}$

- wherein

$C=$ Speed of sound

$V_{0}=$ Speed of observer

$V_{s}=$ speed of source

$\nu _{0 }=$ Original frequency

$\nu {}'=$ apparent frequency

According to doppler's effect

${V}'= V(\frac{V+V_o}{V+V_s})=1392(\frac{343+10}{343+5})$

${V}'=1412 \ Hz$

Option 1)

1332 Hz

Incorrect

Option 2)

1372 Hz

Incorrect

Option 3)

1412 Hz

Correct

Option 4)

1464 Hz

Incorrect

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